CN108418086B - An all-fiber high-order mode Brillouin fiber laser - Google Patents

Abstract

The invention discloses an all-fiber high-order mode Brillouin fiber laser which has an annular cavity structure and comprises a narrow linewidth pump laser, an optical amplifier, a first polarization controller, an optical fiber circulator, a first optical fiber mode selection coupler, a second polarization controller, a single-mode optical fiber, a few-mode optical fiber and a second optical fiber mode selection coupler; the first optical fiber mode selection coupler and the second optical fiber mode selection coupler are cavity mode conversion devices, can realize directional selection coupling of a specific high-order mode in a fundamental transverse mode and a few-mode optical fiber in a single-mode optical fiber, and realize resonance amplification of a high-order mode in a cavity based on Brillouin nonlinear gain of the few-mode optical fiber in an annular cavity, and directly output high-order mode laser. The high-order mode laser output by the invention has good stability and high mode purity, adopts an all-fiber structure, has compact structure and low cost, is easy to integrate with a fiber system, and improves the practicability and reliability of the high-order mode laser.

Description

An all-fiber high-order mode Brillouin fiber laser

technical field

The invention relates to the fields of fiber lasers and optical communications, in particular to an all-fiber high-order mode Brillouin fiber laser.

Background technique

Due to their unique spatial intensity, phase, and polarization distributions, higher-order mode lasing has promising applications and attracted increasing interest. For example, in the field of optical communication, information is modulated on several different high-order modes, that is, mode division multiplexing technology, which can significantly improve the transmission capacity in optical communication. In the field of optical fiber sensing, higher order modes can achieve higher temperature and strain resolution accuracy. In addition, vortex lasers derived from higher-order modes have great potential in quantum and nano-optics, optical manipulation, super-resolution imaging, and laser material processing.

Motivated by these applications, researchers have proposed many methods to generate high-order mode lasing. At present, lasers that generate high-order mode lasing can be roughly divided into two categories: bulk element solid-state lasers and all-fiber lasers. Compared with the former, all-fiber lasers have the advantages of low cost, good flexibility, good stability, small size, and high efficiency. The key components to realize all-fiber lasers are high-efficiency all-fiber mode conversion or selection devices, including dislocation coupling technology, few-mode fiber Bragg gratings, long-period fiber Bragg gratings, and mode-selective couplers. The layout of these mode-conversion or selection devices in all-fiber lasers can be divided into two categories. In the first category, the device is placed outside the resonator and cascaded in the output optical path of the fundamental transverse mode (LP01) laser. In the second category, the device is placed inside a laser cavity containing a single-mode gain medium. But strictly speaking, these two types of lasers are still fundamental transverse mode resonance amplification, rather than the desired high-order mode resonance amplification. In addition, due to the imperfection of the device, these two layouts will also lead to degradation of beam power and quality, and the output high-order modes have low purity. Therefore, it is of great significance to realize a high-efficiency, all-fiber, and low-cost method to obtain high-purity, high-stability, and compact high-order mode lasers.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and provide an all-fiber high-order mode Brillouin fiber laser, based on the Brillouin nonlinear effect, using passive few-mode fiber as the gain medium, and realizing intracavity high-order mode resonance Amplified, high-order mode lasing with high mode purity is obtained directly at the output of the laser. In addition, the laser has the advantages of compact structure, easy adjustment, low cost and high stability.

The purpose of the present invention is achieved through the following technical solutions: an all-fiber high-order mode Brillouin fiber laser, comprising: a narrow linewidth pump laser, an optical amplifier, a first polarization controller, an optical fiber circulator, and a first optical fiber mode selective coupling device, a second polarization controller, a single-mode fiber, a few-mode fiber, and a second fiber mode selective coupler;

Wherein, the optical fiber circulator is a three-port optical fiber circulator provided with a first port, a second port and a third port, and the narrow linewidth pump laser is connected to an optical amplifier through a single-mode optical fiber, and the optical amplifier Connect to the first port of the optical fiber circulator through a single-mode optical fiber, the second port of the optical fiber circulator is connected to the first port of the first optical fiber mode selection coupler through a single-mode optical fiber, and the third port of the optical fiber circulator passes through The single-mode optical fiber is connected to the first port of the second optical fiber mode selective coupler, and the second port of the first optical fiber mode selective coupler is connected to the second port of the second optical fiber mode selective coupler through a few-mode optical fiber to form a ring cavity Structure; the first polarization controller is added to the single-mode optical fiber connected to the first port of the optical fiber circulator, and the second polarization controller is added to the second port of the first fiber mode selective coupler to connect the second The second port of the fiber mode selective coupler is on the few-mode fiber; the third port of the first fiber mode selective coupler outputs laser light.

Preferably, the narrow-linewidth pump laser can be a C-band power-tunable narrow-linewidth semiconductor laser or a narrow-linewidth fiber laser, and the linewidth is lower than 1 MHz.

Preferably, the optical amplifier may be a high-gain erbium-doped fiber amplifier or a 1550nm band semiconductor optical amplifier.

Preferably, in the optical fiber circulator, the pigtail fibers of the three ports are ordinary communication single-mode optical fibers, and the length of the single-mode optical fibers at each port ranges from 0.1 m to 1 m.

Preferably, the few-mode fiber is a 1550nm band few-mode fiber, supports more than 2 modes, and has a length greater than 20m.

Preferably, the first optical fiber mode selective coupler and the second optical fiber mode selective coupler are both 2×2 couplers made by fused tapered single-mode optical fiber and few-mode optical fiber, which can realize single-mode optical fiber Directional selective coupling between the fundamental transverse mode and a specific high-order mode in a few-mode fiber, the first and fourth ports are single-mode fibers, and the second and third ports are few-mode fibers.

The fiber laser of the present invention is a ring cavity structure, and the ring cavity includes a fiber circulator, two fiber mode selective couplers and single-mode fiber and few-mode fiber for connection, wherein the few-mode fiber connecting the two fiber mode selection couplers The optical fiber accounts for more than 99% of the length of the entire ring cavity. The first fiber mode selective coupler and the second fiber mode selective coupler are intracavity mode conversion devices, which can realize the directional selective coupling of the fundamental transverse mode in the single-mode fiber and the specific high-order mode in the few-mode fiber, based on the few-mode fiber in the ring cavity The stimulated Brillouin nonlinear gain realizes the resonant amplification of high-order modes in the cavity, and generates stable and high-purity high-order mode Brillouin laser at room temperature.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. The present invention uses a fiber mode selective coupler as a mode conversion device in a laser resonator cavity, which has low loss and high efficiency.

2. Based on the Brillouin nonlinear gain, the present invention realizes high-order mode intracavity resonance amplification, and the obtained high-order mode laser mode has high purity.

3. The present invention uses a common commercial passive few-mode fiber as the gain medium, which is easy to obtain and popularize.

4. The present invention adopts an all-fiber structure, which is simple and compact in structure, low in cost, easy to adjust, easy to integrate with optical fiber systems, has good output laser stability, and narrow line width, which improves the practicability and reliability of high-order mode lasers.

Description of drawings

Fig. 1 is a schematic diagram of an all-fiber high-mode Brillouin fiber laser of an embodiment.

Figure 2 is a laser power curve diagram.

Fig. 3 is the spectrum diagram of the pump laser and the output Brillouin Stokes laser.

FIG. 4 is a diagram of the far-field light intensity distribution of the output laser.

In Fig. 1: 1-narrow linewidth pump laser; 2-optical amplifier; 3-first polarization controller; 4-fiber circulator; 5-first fiber mode selective coupler; 6-second polarization controller; 7-few mode fiber; 8-second fiber mode selective coupler.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example 1

As shown in Figure 1, a kind of all-fiber high-order mode Brillouin fiber laser of this example includes: a narrow linewidth pump laser 1, an optical amplifier 2, a first polarization controller 3, a fiber circulator 4, a first fiber mode Selective coupler 5 , second polarization controller 6 , few-mode optical fiber 7 and second optical fiber mode selective coupler 8 .

The laser light output by the narrow-linewidth pump laser 1 is amplified by the amplifier 2, and the amplified high-power pump light is injected into the first port 401 of the optical fiber circulator 4, and then injected into the first port 402 of the optical fiber circulator 4. The first port 501 of the optical fiber mode selective coupler 5, after passing through the first optical fiber mode selective coupler 5, the pump light is converted from the fundamental transverse mode of the single-mode fiber in the first port 501 to the first optical fiber mode selective coupler 5 The specific high-order mode of the few-mode fiber in the second port 502 , the high-order-mode pump light generated is injected into the few-mode fiber 7 through the second port 502 of the first fiber mode selective coupler 5 . When the pump light power amplified by the optical amplifier 2 exceeds the Brillouin threshold of the few-mode fiber 7 , a stimulated Brillouin scattering effect occurs to generate Brillouin Stokes light running in reverse. The Brillouin Stokes light generated in the few-mode fiber 7 sequentially passes through the first port 501 of the first fiber mode selective coupler 5, the second port 402 of the fiber circulator 4, and the third port 403 of the fiber circulator 4 , the first port 801 of the second fiber mode selective coupler 8 and the second port 802 of the second fiber mode selective coupler 8 enter the few-mode fiber 7 again to form oscillations in the resonant cavity, that is, to generate a ratio of pump light The frequency of the first-order Brillouin-Stokes light is shifted down, and the Brillouin-Stokes light of this order is output through the third port 503 of the first fiber mode selective coupler 5 .

Between the first polarization controller 3 between the optical amplifier 2 and the first port 401 of the optical fiber circulator 4, and between the second port 502 of the first fiber mode selective coupler 5 and the second port 802 of the second fiber mode selective coupler 8 The second polarization controller 6 jointly controls the polarization state of the pump light and the Brillouin pump light to obtain the maximum Brillouin nonlinear gain.

Narrow linewidth pump laser 1, optical amplifier 2, fiber circulator 4, first port 501 and fourth port 504 of the first fiber mode selective coupler 5, first port 801 and the fourth port 504 of the second fiber mode selective coupler 8 The pigtails (connecting optical fibers) of the fourth port 804 are common communication single-mode optical fibers. Due to the first fiber mode selective coupler 5 and the second fiber mode selective coupler 8 in the fiber loop, the directional selective coupling of the fundamental transverse mode in the single-mode fiber and the specific high-order mode in the few-mode fiber 7 can be realized, so the few-mode The specific high-order mode in the optical fiber 7 will be resonantly amplified, so that the high-order mode laser with high mode purity can be obtained at the third output end 503 of the first optical fiber mode selective coupler 5 .

Narrow-linewidth pump lasers can be C-band power-tunable narrow-linewidth semiconductor lasers or narrow-linewidth fiber lasers, and the linewidth is lower than 1MHz.

The optical amplifier can be a high-gain erbium-doped fiber amplifier or a 1550nm band semiconductor optical amplifier.

Fiber optic circulator, the tail fibers of the three ports are ordinary communication single-mode fibers, and the length of the single-mode fibers at each port ranges from 0.1m to 1m.

The few-mode fiber is a few-mode fiber in the 1550nm band, supports more than 2 modes, and has a length greater than 20m.

Example 2

An all-fiber high-order mode Brillouin fiber laser, the schematic diagram of which is shown in Figure 1. Narrow-linewidth pump laser 1 adopts a narrow-linewidth single-frequency fiber laser in the 1550nm band, with a linewidth of 10kHz and a laser power of 30mW. The optical amplifier 2 adopts a commercial 1550nm band semiconductor optical amplifier, and the amplification power can reach 5W. The optical fiber circulator 4 adopts a commercial three-port single-mode optical fiber circulator. The first optical fiber mode selective coupler 5 and the second optical fiber mode selective coupler 8 are 2×2 couplers made of ordinary communication single-mode optical fiber SMF-28e and commercial two-mode step optical fiber fusion tapered, single-mode optical fiber The conversion efficiency of the LP01 mode to the LP11 mode in the two-mode step fiber is 90%. The single-mode optical fibers in the optical path are all SMF-28e optical fibers. The length of the two-mode step fiber in the ring cavity is 50m, and the length of the single-mode fiber is 0.4m, so the length of the two-mode step fiber accounts for 99.2%. The light splitting ratio of the first port 501 and the third port 503 of the first fiber mode selective coupler 5 is 80:20.

When the amplified pump laser power gradually increases to 780mW, the Brillouin Stokes light in the fiber ring cavity resonates. The pump power continued to increase, and a stable laser output was obtained at the third port of the first fiber mode selective coupler. Figure 2 is the laser power curve, the slope efficiency is 15.6%, when the pump power is 3W, the laser output power reaches 350mW. Figure 3 is the spectrum diagram of the pump laser and the output Brillouin Stokes laser. The output Brillouin laser has a frequency shift of 10.9 GHz relative to the pump light. FIG. 4 is a far-field light intensity distribution diagram of the LP11 mode laser output from the third port 503 of the first mode selective coupler 5 .

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (5)

1. An all-fiber high-order mode Brillouin fiber laser, characterized in that it comprises: a narrow linewidth pump laser, an optical amplifier, a first polarization controller, a fiber circulator, a first fiber mode selective coupler, a second polarization a controller, a single-mode fiber, a few-mode fiber, and a mode-selective coupler for a second fiber; Wherein, the optical fiber circulator is a three-port optical fiber circulator provided with a first port, a second port and a third port, and the narrow linewidth pump laser is connected to an optical amplifier through a single-mode optical fiber, and the optical amplifier Connect to the first port of the optical fiber circulator through a single-mode optical fiber, the second port of the optical fiber circulator is connected to the first port of the first optical fiber mode selection coupler through a single-mode optical fiber, and the third port of the optical fiber circulator passes through The single-mode optical fiber is connected to the first port of the second optical fiber mode selective coupler, and the second port of the first optical fiber mode selective coupler is connected to the second port of the second optical fiber mode selective coupler through a few-mode optical fiber to form a ring cavity Structure; the first polarization controller is added to the single-mode optical fiber connected to the first port of the optical fiber circulator, and the second polarization controller is added to the second port of the first fiber mode selective coupler to connect the second On the few-mode fiber of the second port of the fiber mode selective coupler; the third port of the first fiber mode selective coupler outputs laser light; The first optical fiber mode selective coupler and the second optical fiber mode selective coupler are both 2×2 couplers made by fusion taper of single-mode optical fiber and few-mode optical fiber to realize the fundamental transverse mode in single-mode optical fiber Directional selective coupling with specific high-order modes in few-mode fibers, the first and fourth ports are single-mode fibers, and the second and third ports are few-mode fibers; The all-fiber high-order mode Brillouin fiber laser is a ring cavity laser, in which the few-mode fiber connecting two fiber mode selective couplers accounts for more than 99% of the entire ring cavity length. 2. The all-fiber high-order mode Brillouin fiber laser according to claim 1, wherein the narrow-linewidth pump laser is selected from a narrow-linewidth semiconductor laser or a narrow-linewidth fiber laser with tunable C-band power , with a linewidth below 1MHz. 3. The all-fiber high-order mode Brillouin fiber laser according to claim 1, wherein the optical amplifier is a high-gain erbium-doped fiber amplifier or a 1550nm band semiconductor optical amplifier. 4. all-fiber high-order mode Brillouin fiber laser according to claim 1, is characterized in that, described optical fiber circulator, the tail fiber of three ports is common communication single-mode fiber, and each port single-mode fiber length range is 0.1m to 1m. 5. The all-fiber high-order mode Brillouin fiber laser according to claim 1, wherein the few-mode fiber is a few-mode fiber in the 1550nm band, the number of supported modes is greater than 2 modes, and the length is greater than 20m.